There's a lot to love about Android Wear 5.0.1. The new custom watch face support was just the tip of the iceberg, as we have recently discovered that you can disable Tilt to wake, image searches are more functional, and screenshot support is available but finicky. Another new feature that made it onto Wear 5.0.1 is the new mode switcher for Theatre and Sunlight, both of which are accessible by swiping down on the watch face and scrolling beyond the Mute screen. But it turns out that you don't need so many gestures to enable these modes if you're in a hurry, at least not if your watch has a physical button.
Simply double click the watch's button (verified to work on the LG G Watch R, Gear Live, and Moto 360) to switch Theatre mode on. This will basically mute all notifications while also disabling the Always-On screen and Tilt to wake, essentially rendering your watch as unintrusive as possible. Click the button once to wake the screen and check the time, or double click it again to completely deactivate Theatre mode.
If you triple click the watch's button, you'll activate Sunlight mode, which results in raising the watch's screen to the highest brightness.
You can't switch back, you'll have to manually dial the brightness down. Update: It lasts about 5 seconds, enough time to let you glance at the screen and initiate an action, then switches back to the level it was previously at.
These super handy shortcuts join the previous one where click-and-hold opened the watch's settings. They're definitely going to make my life easier, as I like switching the screen completely off when I'm charging my G Watch R to avoid burn in on the display. There's movies too, but let's face it, I charge my watch a lot more frequently than I go to the movies.